DESCRIPTION: Latent TGF-b binding protein-2 (LTBP-2) is one of four LTBPs, and shares a high degree of identity with fibrillin, a major component of extracellular microfibrils. LTBP-2 has been shown in bovine systems to be an integral component of elastic microfibrils. In humans, mutations in LTBP-2 are associated with a disease sharing similarities with the Marfan syndrome, characterized by skeletal and vascular abnormalities. As its name indicates, LTBP-2 is also a TGF-b binding protein, and may regulate the activity of TGF-bs. In this proposal, the proposed dual function of LTBP-2 will be examined. We have created a targeted deletion in the mouse LTBP-2 gene, eliminating its expression. Mice homozygous for this mutation have an embryonic lethal phenotype. We will ultimately examine the basis for this lethal phenotype. First, we will do several experiments designed to investigate the association of LTBP-2 with microfibrils vs. TGF-b in the developing and adult mouse. The association of LTBP-2 with elastic fibers in the normal mouse will be investigated in situ hybridization and immunolocalization. Association of TGF-b with microfibrils will be examined as well. The LTBP-2/TGF-b interaction will also be investigated. Again, in situ hybridization will be used to determine the spatial and temporal coexpression of LTBP-2 with TGF-b1, -b2 and -b3 in the developing and adult mouse. The specific interaction of LTBP-2 and individual TGF-b isoforms will be investigated in primary explanted murine tissue cultures, and by co-transfection in mammalian expression systems. The binding site on LTBP-2 for TGF-bs will be determined using the same transfection systems. Having defined when and where LTBP-2 is associated with microfibrils vs. TGF-b, we will then examine the basis for the lethal phenotype of the LTBP-2 knockout mouse. Properties of microfibrils will be examined in LTBP-2 -/- embryos, as will the activation state of TGF-b in these embryos. Finally, we will assess whether LTBP-1 can functionally substitute for LTBP-2 in the developing mouse.